In the prior art it is quite common to treat a polymeric material after its formation in order to improve its useful characteristics. Some of the better known treatments include exposure of the film to various forms of radiation, heat treatments including quenching, stretching, buffing, immersion in various chemical liquids, exposure to gaseous mediums, coating and lamination, etc. However, once a film has been coated and made the interior layer of a laminate it has heretofore been difficult, if not impossible, to further treat the interior layer. Accordingly, one object of the present invention is to provide a process for treating the interior layer of a laminate.
One reason why a film may be coated or laminated before treatment is completed is that it is often more economical to coextrude several layers of a tubular material in a single die or in a series of coextrusion dies and then stretch the coextruded tubing into film thicknesses. This way the film need only be handled once and all layers will be uniformly stretched and, in some instances, uniformly oriented. However, further treatment of an interior layer is not readily accomplished and it is another object of the present invention to provide a method of treating interior layers of a coextruded or extrusion laminated film.
In the prior art it has been found that the properties of nylon or polyamide film will improve beneficially with treatment by or exposure to water. For example, in U.S. Pat. No. 3,397,263 a process is disclosed for steam treating chill-cast nylon film to remove structural irregularities such as uneven film thicknesses. Likewise, in U.S. Pat. No. 3,651,200 a method is disclosed for orienting nylon film while it simultaneously adsorbs water. Therefore, it is still another object of the present invention to provide a method whereby a laminate having an interior layer of nylon may be beneficially treated with water.
The foregoing and many other objects will become obvious to those skilled in the art from the following summary and description of the invention.